(Western) Psychology has primarily dealt with the study of individuals, and just lately started to research the dynamics and influences groups have on individuals in a field called Social Psychology. In eastern (collectivist) cultures, people define themselves mainly in relation to their social situation, whereas people in Western societies prefer to construct their identity by individual attributes like attitudes and traits.
Probably one of the earliest approaches to understand group phenomena can be found in Edward Bernays book Propaganda. Bernays' ideas were first applied by the Nazi propaganda minister Goebbels, yet survived in the advertising industry until today. The form of collaboration achieved by propaganda, political as well as commercial, is hardly deliberate, but constitutes an influence that reaches into most aspects of an individuals life.
Humans are social beings, and as such dependent on the opinion of their peers. Muzafer Sherif (1936) and Solomon Asch (1951) conducted experiments to determine the amount of conformity that can be reached in group situations. They found that social norms can arise which do not relate to the individuals perception of events, or even contradict them. Asch presented a group of participants with a standard line, which then had to be identified among a sets of lines with different lengths. Only one member the group was the test candidate, the others confederates. If the confederates gave a consistent wrong answer, one third of the participants adjusted their reply to this fake consent.
This is just one example of what is now called Groupthink, a principle that seems to occur naturally in group situations. Groupthink speeds up decision making for the individual, but it is detrimental if the consent found is invalid. One way of preventing Groupthink, or at least to improve the quality of consent, is to institutionalize dissent, eg. by nominating a devil's advocate or actively encouraging self and other criticism.
Groups can always polarize into majorities and minorities, and in collaborative situations this can easily impair to find the best solution for a given problem. Encouraging dissent and using facilitation processes (such as the Talking Stick) can increase the quality of the collaborative results.
Each group goes typically through five phases:
Forming of a group can either be deliberate (deciding to form a band, gang, theater group) or accidental (being assigned to a work group, being among the witnesses of an event). At this time, only a rough idea of the collaborative product exists, and hardly any idea about the group roles, norms and strategies. It is the stage where group members get to know each other, and mostly depend on a leader (which is either assigned or initiated the group formation)
In the Storming stage of a group dissent and discussion let methods and roles emerge to solve the given (or chosen) task. The leader role might be challenged, and, depending on the size of the group, coalitions form.
Once goals and procedures have been agreed on, the Norming stage is dominated by reaching consent, and setting up the norm of a given group. The group cohesion increases, and it becomes part of the identity of its members.
Goals, procedures, roles and norms are now in place, and in the Performing stage the group produces its collaborative results, which might be a song, a theater play, a campaign or whatever the chosen task was.
The Adjourning stages sets in once the task is completed (if it was a single task), or the social cohesion is not sufficient to produce more of the same (eg in artistic contexts). However, if the group ever reached a performing stage, it will remain a part of the emotional memory of its members.
These stages are not clearly separated, and depending on the group size and task duration appear more than once. Wikipedia, as a collaboration with open end, is certainly in all of these stages: New members participate (Forming), might challenge or ignore the existing norms (Storming), which might lead to an adaption of new norms (Norming), and some people might discontinue their participation for various reasons (Adjourning), while the number and quality of articles there continually increases (Performing).